1. Field of the Disclosure
Embodiments of the present disclosure relate generally to apparatuses and systems used to perforate a subterranean formation, and methods of using the same. Other embodiments relate to perforation of a subterranean formation in order to induce and/or facilitate downhole separation of subterranean fluids produced therefrom.
2. Background Art
Once a wellbore is drilled into a formation with conventional drilling methods, the wellbore is usually completed by positioning a casing string within the wellbore. The casing string increases the integrity of the wellbore, and also provides a path to the surface for fluids to flow from the formation to the surface. The casing string is normally made up of individual lengths of relatively large diameter tubulars that are secured together by any suitable method known to one of skill in the art, such as screw threads or welds.
Typically, the casing string is cemented to the wellbore by circulating cement into the annulus defined between the casing string and the wellbore. The cemented casing string is subsequently perforated to establish fluid communication between the formation and the interior of the casing string so that the valuable fluids within the formation may be produced to the surface. Perforating has conventionally been performed by lowering a perforating gun (or other comparable device) down inside the casing string.
A perforating gun may be constructed to be of any length, and the gun is typically lowered within the casing on a wireline or other device to a point adjacent a zone of interest. Commonly, perforating guns are run into the wellbore via lines that also convey signals from the surface in order to fire the gun, and may include the use of coiled tubing or slicklines. Slicklines, which do not require surface communication to fire the gun, use a mechanism on the gun to fire the charges upon reaching, for example, a certain temperature, pressure, elapsed time, etc.
Once the gun is at a desired location, an explosive charge connected to the gun is detonated in order to penetrate or perforate one or more of the casing string, the wellbore, the formation, etc. A typical explosive charge may fire and result in a high-pressure, high-velocity jet that creates the perforation. The extremely high pressure and velocity of the jet cause materials, such as steel, cement, rock formations, etc. to flow plastically around the jet path, thereby forming the perforation. The perforations, including characteristics and configurations thereof, have significant influence on the productivity of the well. Thus, the choice and/or configuration of the perforating charge are of importance, including the direction of the resultant charge.
FIGS. 1A-1D together depict an example of a conventional perforation system and perforating tool 100. The perforation tool 100 may be positioned within a wellbore 102 adjacent to a casing string 104, which may be near a zone of interest within the formation 112. A tubestring 107 connected to a power source via wireline (not shown), or that has any other kind of operable detonation device, may be used to detonate one or more charges 106 mounted on the tool 100.
Typically, a perforation tool 100 may be, for example, thirty feet long with a series of charges 106, usually located on one or more sides of the tool 100. The design of the charges 106 depends on a number of factors, such as the type of formation, the desired production zone, the design of the zone, etc. The tool 100 may have charges 106 configured to provide, for example, one perforation per foot, one perforation per two feet, two perforations per foot, etc., and the charges 106 are usually spaced apart and mounted in such a way that the charges 106 are aimed toward the casing string 104 in order to shoot toward the casing. Upon firing, the charges 106 detonate and fire a fluid jet 109 (or other comparable discharge or propellant) in at least one outward radial direction 110 toward the casing 104, thereby creating perforations 114.
Previously, the location of the perforation(s) did not matter as long as fluids were produced from the formation. Typically, radial perforations are positioned as close as every six inches to about every two feet; however, this becomes problematic because close perforations interfere with the drain radius, as well as with each other. Fluids that enter the wellbore enter in an uncontrolled and violent/turbulent fashion into a small singular area that makes production of the fluids difficult.
To help production, a pump may be disposed below these perforations. However, when subterranean fluids are produced, there is usually gas and liquid mixed together, such that the liquid phase will often have small bubbles (i.e., gaseous phase) entrained in the liquid, which makes it extremely difficult to pump the liquid. In addition, it has been found that as fluid comes out of the perforations, the fluids are subject to immediate boiling in the wellbore, hence forming even more gas. As a result of a substantial amount of turbulence from conventional perforation and because of boiling, vast amounts of gas and bubbles end up being carried down in the liquid phase toward the pump.
The bubbles of the gas become very transient, in that the bubbles create pulsing and slugging in the well. Therefore, it becomes necessary to put the pump far enough down that pulsation does not reach the pump. Because the liquid may carry the gas down the wellbore to great depths, it is often necessary to place the pump at a distance greater than 1000 feet. Alternatively, or additionally, in order to separate bubbles it may become necessary to substantially slow production rates in order to guarantee minimal adequate separation from buoyant forces.
Sometimes it has been beneficial to provide an extra rotational force that promotes extra separation with the fluids. The rotational force causes, for example, bubbles to collect towards the center where the bubbles can grow in size. Larger bubbles are desired toward and in the center because larger bubbles have the tendency to lift their way through the liquid phase much more easily than the small bubbles.
Several attempts have been attempted to provide a mechanical rotational force within a wellbore. For example, some downhole devices, such as centrifuges or cyclones, try to get the liquid to swirl in order get a spinning effect and hopefully some separation of the gas. However, these devices are cumbersome within the wellbore, and are also problematic in that they do not provide sufficient swirling. Without sufficient swirling the gas cannot escape from the liquid, and the bubbles are carried down to the pump inlet.
Thus, there is a need to easily promote sufficient swirling of the formation fluids in the wellbore that is both economic and unencumbered. There is a need to increase production rates of fluids produced from perforated wellbores, as well as to reduce the length between perforations and downhole-disposed pumps. There is a great need to perforate a formation to induce subterranean fluids to enter tangentially, thereby creating a natural vortex and/or cyclonic motion. There is a need to separate formation fluids in order to easily produce liquids from a subterranean formation.